With 9 of 10 tablet and smartphone owners using their gadgets to enhance their television-watching experience, Silicon Valley startups are rushing in to capitalize on the craze — known in the business as “second screens.”

Get Glue, Yap.tv, Shazam, Yahoo!’s IntoNow and Miso are just four of the firms seeing rapid growth in the second-screen sector.

Get Glue, one of the “veterans,” having launched in 2008, now has more than 2 million users who are “checking in” to entertainment.

It has more than 350 million data points for its users — who appear to have a hunger for added TV content information.

For example, during the April 1 season premiere of HBO’s “Game of Thrones,” 50,000 second-screen user check-ins briefly crashed servers.

During last season’s premiere, just 8,000 users checked in.

According to Mark Ghuneim, founder and CEO of Trendrr, a social-media platform, social television creates “shared experiences and proximity — to both your friends and characters in a show,” which benefits advertisers, networks and consumers.

This engagement metric is the core of second-screen television. Social apps like Viggle have insight into engagement, which is quickly becoming indispensable to the television industry.

Viggle, a public company, relies on audio verification to identify which program users are watching on live TV or DVR. It checks them into a particular show, thus earning the user “points” — the currency system of Viggle — that they can then redeem for real rewards, like gift cards or movie tickets.

A free loyalty program for television that launched in February, Viggle, and Zeebox, a new UK-based app that will be launching in the US this summer, are quickly proving themselves valuable to advertisers, networks and consumers.

They’re doing what their predecessors continue to do well, but with even more advanced technologies and enhanced business models and functionalities.

“[Television] is a $50 billion industry,” Anthony Rose, co-founder of Zeebox, explains. “The ad business in television is going to be revolutionized and taken into a new age.”

“Second screen,” he added, “is going to make that happen.”

A recently released report from Nielsen found that 88 percent of people who own tablets and 86 percent of those with smartphones in the US have used their devices at least once while watching television in the past month.

These new tech startups are determined to capitalize on such behavioral trends.

Consumers are clearly hungry, signifying room for more advanced apps in the second-screen space.

Viggle comes into play at the intersection of the consumer, television networks, advertisers and rewards partners.

Though ad-supported, Viggle focuses on “cost per engagement” to help advertisers find that level of “richer, deeper engagement,” notes Vice President of Marketing Jason Reindorp.